The plant disclosed in Patent Document 1 listed below can be given as an example of a plant including a plurality of steam turbines. This plant includes a boiler that generates steam, a plurality of steam turbines driven by the steam from the boiler, and a condenser that condenses steam exhausted from the steam turbines back into water. As the plurality of steam turbines, the plant includes a high-pressure steam turbine, a mid-pressure steam turbine, and a low-pressure steam turbine. Meanwhile, the boiler includes a steam generator that generates steam, a superheater that superheats the steam generated by the steam generator, and a repeater that reheats the steam.
The superheater of the boiler and a steam inlet of the high-pressure steam turbine are connected by a main steam line. A main steam stop valve and a main steam regulator valve are provided in the main steam line. A steam outlet of the high-pressure steam turbine and a steam inlet of the mid-pressure steam turbine are connected by a reheat steam line that conducts steam exhausted from the high-pressure steam turbine to the steam inlet of the mid-pressure steam turbine via the reheater of the boiler. A reheat steam stop valve and an intercept valve are provided in a part of the reheat steam line downstream from the reheater. A steam outlet of the mid-pressure steam turbine and a steam inlet of the low-pressure steam turbine are connected by a low-pressure steam line. A condenser that condenses steam exhausted from the low-pressure steam turbine back into water is provided in the low-pressure steam turbine. The condenser and the boiler are connected by a feed water line.
The main steam line and a part of the reheat steam line upstream from the reheater are connected by a high-pressure turbine bypass line. A high-pressure bypass valve is provided in the high-pressure turbine bypass line. A part of the reheat steam line upstream from the re heater and the condenser are connected by a ventilator line. A ventilator valve is provided in the ventilator line.
According to this plant, at startup, with the high-pressure turbine bypass valve and the ventilator valve in an open state, the high-pressure main steam stop valve opens and the high-pressure steam regulator valve gradually opens. During the start of circulation in the high-pressure steam turbine, windage loss of the high-pressure steam turbine causes the temperature of exhaust steam to rise. Accordingly, the rise in the temperature of the exhaust steam is suppressed by opening the ventilator valve, connecting the condenser to the steam outlet of the high-pressure steam turbine, and increasing a pressure difference between the inlet side and outlet side of the high-pressure steam turbine. The ventilator valve is closed upon a flow rate of high-pressure steam flowing into the high-pressure steam turbine, or in other words, a load of the high-pressure steam turbine reaching a predetermined load.